Answers for "groupby month pandas dataframe datetime"

pandas group by month

b = pd.read_csv('b.dat')
b.index = pd.to_datetime(b['date'],format='%m/%d/%y %I:%M%p')
b.groupby(by=[b.index.month, b.index.year])
# or
b.groupby(pd.Grouper(freq='M'))  # update for v0.21+
# or
df.groupby(pd.TimeGrouper(freq='M'))

group by month and day pandas

max_temp = dfall.groupby([(dfall.Date.dt.month),(dfall.Date.dt.day)])['Data_Value'].max()

group by dateime pandas

df['date_minus_time'] = df["_id"].apply( lambda df : 
datetime.datetime(year=df.year, month=df.month, day=df.day))	
df.set_index(df["date_minus_time"],inplace=True)